1. Field of the Invention
The present invention relates to electroplating of electrodes. In particular the invention relates to processes for preparing electrodes for electroplating as well as processes of electroplating of electrodes.
2. Description of the Related Technology
Microscopic holes, cavities or indentations in a working electrode can trap air when the working electrode is immersed in electroplating solution for electroplating. The trapped air may impede or prevent desired metal deposition in the microscopic holes of the working electrode. For example, bubbles can cause pinholes in the plated metal layer. The problem is especially troublesome when the working electrode is designed to have millions of deep microscopic holes and it is desired to completely fill every one of these microscopic holes with electroplated metal. This problem is encountered, for example, when making microwire glass for electronic devices that utilize microelectrode arrays from a glass microchannel plate.
A glass microchannel plate (MCP) is shown in FIG. 1. The MCP 11 consists of a glass plate 11 with a high density of open microscopic channels 12 that extend through the plate 11 from one side to the other. The empty microchannels 12 are typically uniform in size, extremely straight and parallel to each other, and arranged in an orderly array. A MCP 11 with a microchannel diameter of 5 micrometers typically has approximately 1.8 million separate microchannels 12 per square centimeter.
Commercially available microchannel plates 11 (e.g., from Collimated Holes, Inc.) with 5 micrometer diameter microchannels 12 can be 500 to 1.000 micrometers thick. When the microchannel plate 11 is immersed in an electroplating bath, a bubble in any microchannel 12 can partially or fully block the deposition of metal via electroplating in that microchannel 12. Because of both the very high aspect ratio (the ratio of microchannel length to diameter can be as high as 200:1) and the huge number of microchannels 12 in a square centimeter of a MCP 11, there is a high propensity for trapped air to form bubbles in some of the microchannels 12 when the MCP 11 is immersed in a liquid such as an electroplating bath.
In theory the force of capillary draw should be sufficient to force the electroplating liquid to fill the microchannels 12, but in practice this does not happen in all of the microchannels 12. Incomplete deposition of metal in the microchannels 12 can compromise the integrity and performance of any device which incorporates “microwire glass” (MWG). MWG is a glass microchannel plate 11 that has the microchannels 12 filled with metal to form an array of microwires.
To make microwire glass (MWG), a microchannel plate 11 is mounted in such a way that metal electroplating will start from one end of the microchannels 12 (the “start-side” of the MCP 11) and proceed to fill the microchannels 12 with metal all the way through to the opposite end of the microchannels 12 (the “finish-side”). The MCP 11 is typically sealed in a mount such that the only pathway for metal deposition by electroplating is through the microchannels 12. A bubble anywhere inside the length of any microchannel 12 can impede or block electrodeposition in that microchannel 11.
Accordingly, there is a need in the art to provide an improved process for electroplating of microchannels to reduce or eliminate defects which may be caused by gas bubbles present during the electroplating process.
This and other objects of the present invention will be apparent from the summary and detailed description which follow.